Kirkiite is a rare lead-bismuth sulfosalt typically found as microscopic grains or small aggregates within hydrothermal ore deposits. It is best identified through lab analysis or X-ray diffraction, as it is macroscopically indistinguishable from other lead-gray sulfide minerals found in similar geologic settings.

Hardness

3.5

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrareLead-Bismuth Sulfosalt Group family

Kirkiite

Hardness: 3.5
Luster: Metallic
Streak: Black
Transparency: Opaque

Is this kirkiite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch kirkiite with a known reference. Kirkiite sits at Mohs 3.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: black.
3
Read the luster
Hold the specimen under a strong light. Luster: metallic.
4
Match the color range
Compare against the expected color range: tin white.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: microscopic crystals, pseudo hexagonal, twinning common.

Often confused with

Kirkiite vs. its common look-alikes, and how to tell them apart in the field.

mineral

Galena

Mohs 2.5-2.75

How to tell apart: Kirkiite is noticeably harder (Mohs 3.5 vs. 2.5-2.75); streak differs, so Kirkiite leaves black, Galena leaves lead-gray.

Often found alongside kirkiite

Minerals reported to co-occur with kirkiite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: Pb₁₀Bi₃As₃S₁₉
Mohs hardness: 3.5
Density: 6.80 g/cm³
Colors: Tin white
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Monoclinic
Crystal habit: Microscopic crystals, pseudo hexagonal, twinning common
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: In a hydrothermal Pb-Zn deposit (Kirki, Greece); in a volcanic fumarole, formed at about 470 °C (Vulcano, Italy)

Where rockhounds find kirkiite

Classic worldwide localities

Aghios Philippos Pb-Zn deposit, near Kirki, Thrace, Greece (type locality)
La Fossa crater, Vulcano, Lipari Islands, Italy

Field-hunting tip

Where it forms: In a hydrothermal Pb-Zn deposit (Kirki, Greece); in a volcanic fumarole, formed at about 470 °C (Vulcano, Italy). If you start seeing cosalite, bismuthinite, bismuthian jordanite in float, you are in the right ground. Typical habit: microscopic crystals, pseudo hexagonal, twinning common. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify kirkiite?+

Mohs hardness is 3.5. Luster: metallic. The streak is black. Common colors include tin white.

Where is kirkiite found?+

Notable localities include Aghios Philippos Pb-Zn deposit, near Kirki, Thrace, Greece (type locality); La Fossa crater, Vulcano, Lipari Islands, Italy.

Is kirkiite safe to handle?+

Kirkiite contains arsenic and lead and calls for real care. Contains lead and bismuth; handle with care and wash hands after contact. Avoid inhaling dust or powder.

What rocks look like kirkiite?+

Kirkiite is most often confused with Galena, Cosalite, Kobellite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with kirkiite?+

Kirkiite commonly co-occurs with Cosalite, Bismuthinite, Bismuthian jordanite, Seligmannite, Levyclaudite, Sphalerite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does kirkiite form in?+

Where it forms: In a hydrothermal Pb-Zn deposit (Kirki, Greece); in a volcanic fumarole, formed at about 470 °C (Vulcano, Italy). Working float back to the host body is the standard way to chase a fresh occurrence.

What is kirkiite used for?+

Kirkiite is used in collector.

Find kirkiite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.